This invention relates generally to plasma display panels and their construction. Specifically, the invention relates to a plasma screen comprising a front plate which comprises a glass plate on which a dielectric layer and a protective layer are deposited, and comprising a carrier plate coated with a fluorescent layer having a rib structure, which divides the space between front plate and the carrier plate in plasma cells which are filled with a gas, and further comprising one or more electrode arrays on the front plate and the carrier plate for generating silent electrical discharges in the plasma cells.
Plasma screens enable color pictures with high definition, large screen diagonals and have a compact structure. A plasma screen comprises a gas-filled sealed glass cell with grid-like arranged electrodes. By applying an electric voltage, a gas discharge is caused which mainly generates light in the vacuum ultraviolet range. Fluorescence transforms this VUV light into visible light and the front plate of the glass cell emits this visible light to the viewer.
Plasma screens are subdivided into two classes: DC plasma screens and AC plasma screens. With the DC plasma screens the electrodes are in direct contact with the plasma. With AC plasma screens the electrodes are separated from the plasma by a dielectric layer.
In principle, two types of AC plasma screens are distinguished: a matrix arrangement and a co-planar arrangement of the electrode arrays. In the matrix arrangement the gas discharge is ignited and maintained at the point of intersection of two electrodes on the front plate and carrier plate. In the coplanar arrangement the gas discharge between the electrodes on the front plate is maintained and at the point of intersection ignited with an electrode, a so-called address electrode on the carrier plate. The address electrode is located in this case beneath the fluorescent layer. Fluorescent substances which emit different colors are separated by barriers so that only light of the desired color is generated.
For a sufficient picture contrast in daylight it is important for a plasma screen to have a high luminance and the least possible reflection of external light. The parameter of this property is the Luminance Contrast Performance (LCP):   LCP  =            luminance      ⁢              xe2x80x83            ⁢              (        L        )                            reflection        ⁢                  xe2x80x83                ⁢                  (          R          )                    
An enhancement of the contrast and thus an improvement of the LCP value can be achieved, for example, by depositing a so-called black matrix on the barriers or on the areas of the front plate opposite the barriers. Such a black matrix reduces the reflection of ambient light so that the picture contrast is enhanced when the surrounding light is increased.
JP 10-269951 discloses a plasma screen with a black matrix on the front plate which absorbs visible light incident from outside and at the same time reflects light incident from inside. This is achieved in that the side of the black matrix turned away from the viewer is coated with a layer which reflects visible light. This reflecting layer may then be provided directly on the black matrix or parallel therewith with a certain distance.
In either case the black matrix and the reflecting layer are embedded in the dielectric layer, which consists of PbO-containing glass. Under the drastic circumstances during the manufacturing of plasma screens, more particularly high temperatures, this may lead to undesired reactions between the black matrix and/or the reflecting layer with the dielectric layer, which reactions result in discolorations and thus certainly in a reduction of the reflection properties of the reflecting layer.
Therefore, it is an object of the present invention to provide a plasma display panel or screen which produces a picture with improved contrast.
The object is achieved by a plasma screen comprising a front plate which comprises a glass plate on which a dielectric layer and a protective layer are deposited, comprising a carrier plate coated with a fluorescent layer having a rib structure, which divides the space between front plate and carrier plate in plasma cells which are filled with a gas, and comprising one or more electrode arrays on the front plate and the carrier plate for generating silent electrical discharges in the plasma cells and comprising a structured black matrix which is coated with a reflecting layer between dielectric layer and protective layer on the side turned away from the viewer.
The arrangement of the protective layer and the structured black matrix on which is coated with a reflecting layer is deposited on the side turned away from the viewer, provides that on the dielectric layer and not in the dielectric layer a reaction of the dielectric layer with the reflecting layer is avoided and reactions with the structured black matrix are minimized.
A further advantage of this arrangement is that the reflecting layer on the structured black matrix is closer to the discharge cell. This increases the intensity of the generated light because it is reflected directly and not first passes through the dielectric layer where it may be partially absorbed.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.